Actuator with limiting mechanism and torque limiting clutch



V. A. HOOVER April 4, 1967 I ACTUATOR WITH LIMITING MECHANISM AND TORQUELIMITING CLUTCH Original Filed Sept. 5, 195'? IN VEN TOR.

26 sch- United States Patent 3,312,916 ACTUATOR WITH LIMITING MECHANISMAND TORQUE LIMITING CLUTCH Vaino A. Hoover, 1433 San Vicente Blvd.,Santa Monica, Calif. 90402 Original application Sept. 5, 1957, Ser. No.682,121, new Patent No. 3,087,105. Divided and this application June 13,1962, Ser. No. 202,169

5 Claims. (Cl. 335-44) This invention relates generally toelectromechanical actuators, and more particularly to an actuator ofthis type having a rotational output and incorporating means forlimiting the torque applied to its output shaft and means for limitingthe movement of that shaft.

The present application is a division of my prior co pending applicationentitled, Electromechanical Actuator with Limiting Mechanism, Ser. No.682,121, filed Sept. 5, 1957, now Patent No. 3,087,105.

Electromechanical actuators have been found to be very effective meansfor actuating movable parts. One of the principal applications of theseactuators is in modern aircraft, where they are used for suchpurposes'as the actuation of trim tab and the lik'e. Such actuators alsoserve effectively in many other-applications, including industrialautomation.

In most applications of actuators of the subject type, it is anoperational requirement that movement of the output shaft be accuratelycontrolled within predetermined limits. To achieve this, the actuator isequipped with a limiting mechanism, which serves to terminate theoperation of the actuator in a given direction, when the driven devicehas reached a corresponding limit position. It will be readilyappreciated that, particularly in aircraft applications where amalfunction is potentially disastrous, the operation of the actuatormust be as foolproof as possible. Moreover, the operation of thelimiting mechanism is especially crucial. A malfunction of thatmechanism may, for instance, cause jamming of the driven devide oroverheating of the drive motor, besides possible mechanical failure ofany one of the parts of the actuator and driven device due to excessivetorque.

Therefore, by way of summary, it is extremely important in suchactuators not only that the limiting mechanism be as troublefree aspossible, but also that additional protective means be provided, whichwill eliminate the possibility of excessive torques and resulting damageto both the actuator, and the driven device in the event a malfunctionshould occur. Such protective means may in some cases be providedexternally of the actuators as, for instance, between the output shaftof the actuator and the driven device. However, in most cases, it isdesirable, because of practical considerations, to incorporate them inthe actuator itself. 7

Another requisite feature of actuators in aircraft and many otherapplications is that they be constructed and arranged so that the limitpositions of the output shaft can'be adjustably established andcoordinated with the mechanical limits of the driven device. This isnecessary for the reason that the part to be actuated normally has somemanufacturing tolerances. Moreover, additional tolerances frequentlydevelop during assembly. To compensate for such tolerances and insurethat the limit positions of the actuator and its associated drivendevice coincide, it is necessary to provide for final adjustment afterassembly. In somewhat similar regard, it is frequently desirable toadjustably establish the maximum torque which is applied to the outputshaft. Some driven devices are highly susceptible to damage by virtureof eX- cessive t'orques, and, therefore, in those cases accurate controlof the maximum torque is of vital importance.

3,312,916 Patented Apr. 4, 1367 ice Moreover, an actuator with a torqueadjustment feature is capable of being used in a variety of differentapplications. Further ope-rational requirements of such actuators inaircraft applications are that, in addition to the above capabilities,the device be 'suificiently sturdy to withstand sustained vibration andrapidly fluctuating atmospheric conditions, and be relatively lightinweig-htx i It is, therefore, a major object of this invention toprovide an electromechanical actuator, which satisfies all of the aboverequirements. 3 J Another, more specific object is to provide anelectromechanical actuator with a limiting mechanism for controllingmovement of its output shaft within predetermined limits, the mechanismincorporating means for protecting both the actuator and the drivendevice from damage in the event of a malfunction of the limitingmechanism.

It is a further object of this invention to provide an actuator of thetype, described, having an improved torque limiting clutch for limitingthe torque applied to the output shaft.

A related object is to provide an actuator of the type described with atorque limiting clutch, which is conveniently adjustable from theexterior of the actuator for accurately establishing the maximum torqueapplied to the output shaft.

Another object of this invention is to provide an electromechanicalactuator capable of accomplishing the foregoing objects, and furthercharacterized in that his relatively small in size and light in weight,yet sufficiently rugged to withstand the rigors of use in aircraftinstallation.

These and other objects, features, and advantages of the invention willbe better understood. by referring to the following detailed descriptiontaken in conjunction with the accompanying drawing ofv an illustratedembodiment thereof, in which:

FIGURE 1 is a side view, partly in elevation and partly in section,showing the actuator of the invention; v

FIGURE 2 is a sectional view takenalong the line 2-2 of FIGURE 1 andillustrating in elevation certain operating parts of the limitingmechanism of-theactuator;

FIGURE 3"is an enlarged sectional view of the area encircled by the line3 in FIGURE 1, showing the adjustable feature of the torque limitingclutch;

7 FIGURE 4 is a sectional View taken on the lin 4- of FIGURE 1; and

FIGURE 5 is an exploded view of certain cooperating parts of the torquelimiting clutch.

Referring to the drawing, and in particular to FIGURE 1 thereof, numeral10 designate the actuator of the invention. The actuator 10 includesgenerally a reversible electric motor 12, a magnetic clutch and brakeunit 14, reduction gearing 16, a torque limiting clutch 18, and alimiting mechanism 20.

Briefly, the motor is adapted to be energized so as to alternately drivethe output shaft 22 in clockwise and counterclockwise directions, asviewed from the right hand end of FIGURE 1, and thereby move a drivendevice (not shown) between extended and retracted positions. Connectedto the output shaft 22 at its inner end is the limiting mechanism 20,which serves to de-energize the motor 12 when the output shaft has movedin either direction to limit positions, which correspond to themechanical limits at the extended and retracted positions of the drivendevice. The function of the torque limiting clutch during such operationis, as suggested above, to insure that the torque applied to the outputshaft 22 does not exceed a predetermined level. 'It is to be noted atthe outset that the presentinvention is primarily concerned with theconstructions and arrangethe shaft.

ments and operational features of the torque limiting clutch 18 and thelimiting mechanism 20.

The function of the magnetic clutch and brake unit 14 is to detachablycouple the motor 12 to the reduction gearing 16. A unit of the typedisclosed in my U.S. Patent No. 2,618,368 entitled, Magnetic Clutch, andissued Nov. 18, 1952, may be used to advantage for this purpose. As thepatent reveals, the main advantage of the magnetic clutch and brake unitis to automatically operate when the output shaft has been driven to adesired position and the motor de-energized, to hold the shaft againstmovement under the influence of externally applied loads. The unit 14has further utility in selected applications, where it may beautomatically actuated to detach the motor from its reduction gearingand thereby permit two actuators, when driven as a pair, to be driven byone motor, should one motor fail.

} The torque limiting clutch 18 is contained within a housing 23 whichrotatably mounts the output shaft 22. Freely rotatable on the outputshaft 22 adjacent its inner end 24 is a worm wheel 26 which, in turn, isdriven by a cooperating worm 28 coupled to the reduction gearing 1 6. Amounting sleeve 30 is fixed to one face of the worm wheel 26 and extendsaxially therefrom toward the driving end of the shaft 24 in concentricrelationship therewith. It will be understood that the shaft 22 and thewheel-sleeve assembly 26, 30 are rotatable both with respect to thehousing 23 and with respect to one another. Bearing support of thesemembers is enhanced by a plurality of ball bearings 32.

Coupling of the shaft 22 to the sleeve 34) is achieved by means of aplurality of cooperating clutch disks including shaft :disks 34 andsleeve disks 36. The disks 34 and 36 are disposed alternately in face toface relation and keyed to the shaft 22 and sleeve 30, respectively. Bypressing the engaging faces of thedisks 34 and 36 in frictionalengagement with one another, a frictional coupling between the parts isafforded.

Each of the shaft disks 34 has an inside diameter just slightly greaterthan the diameter of the shaft 22 and is receivable thereon. In order tokey the disks 34 to the shaft, the former are provided with a pluralityof angularly 'spaced and radially inwardly extending splines or fingers38 received in mating splineways or grooves 49 in As may be seen inFIGURE 5, each of the shaft disks 34 is formed with annular shoulders 42(or a single shoulder in the case of the end disks) adjacent theirperipheries. Supported on the shoulders of adjacent disks 34 are thesleeve disks 3 6, which have an internal diameter approximately-equal tothe diameter of the annular shoulders 42. Referring to FIGURE 3, it maybe seen that the thickness of each sleeve disk 36 is slightly greaterthan twice the width of a shoulder 42 on the shaft disk 34. Connectionof the sleeve disks 36 to the sleeve 30 is achieved by providing aplurality of angularly spaced and radially outwardly extending splinesor fingers 44 on the periphery of each disk 36 and mating splineways orgrooves 46 in the inner periphery of the sleeve 30. Accordingly, theshaft disks 34 rotate with turn, correspondingly changes the frictionalcoupling between the sleeve 30 and output shaft 22.

Movement of the keys 54 in their respective grooves 56 is effected bymeans of a flanged nut 58 threadedly engaged on the output shaft 22. Theannular end face of the nut 58 bears against the outer one of a pair ofrings 60 interposed between the keys 54 and nut. Tightening of the nut58 on the shaft in opposition to the force of the springs 48 and 52, ofcourse, serves to advance the keys 54 to the left in the drawing andincrease the torque level at which slippage of the clutch will takeplace, whereas backing off the nut has the reverse effect.

It will be understood that in normal operation of the actuator 10, thefrictional engagement of thedisks 34 and 36 serves to couple the sleeve30 to the output shaft 22. Accordingly, when the motor 12 operates torotate the worm 28 and drive the worm wheel 26, movement of the outputshaft 22 takes place. However, when the torque load on the shaft 22increases above a predetermined level, adjustably established by varyingthe spring pressure in the above manner, slippage takes place betweenthe disks 34 and 36. In this latter condition, the wheel-sleeve assembly26, 30 continues to rotate, but the output shaft 22 remains stationary.In order to permit slippage between the disks 34 and 36 without damageto them, adjacent disks preferably are made of different materialshaving good bearing characteristics as, for example, bronze and steel.

The limiting mechanism 20 is contained within a housing 64 secured tothe housing 23 at the end opposite the output shaft 22. In general, themechanism 20 comprises a pair of switches 66 and 68 electricallyconnected to the motor 12 and adapted to be actuated by associated cams7t) and 72 at predetermined limit positions of the actuator tode-energize the motor.

Mounted within the housing 64 ata location parallel to, but offset from,the axis of the worm wheel 26 and output shaft 22 is a cam shaft 74. Theshaft 74 is driven shaft 74 in side by side relation.

the shaft 22, whereas the sleeve disks 36 rotate with the sleeve 30.

Frictional engagement of the cooperating disks 34 and 36 is establishedby providing spring washers on the shaft '22 at opposite ends of thedisk configuration. More specifically, a spring washer 48 is provided atthe inner end of the configuration and is compressed between a flangedcollar secured on the shaft 22 and the terminal shaft disk 34. At theopposite end of the configuration, a spring washer 52, here shown as adouble washer for added resiliency, is disposed in compression betweenthe shaft disk 34" and a plurality of keys 54. The keys 54-are axiallymovable in axial grooves 56 in the periphery of the shaft, so as toenable them to be moved to adjust the compression of the springs 48-and52. As will be appreciated, adjusting the compression of the springs, in

by the worm wheel 26 through a pair of meshing spur gears 76 and 78, thegear 76 being secured to the worm wheel 26 and the gear 78 being fixedon the end of the cam shaft 74. As may be seen in FIGURE 1, the wormwheel 26 is formed with a drum portion 80, which projects axially fromthe face of the wheel opposite the mounting sleeve 30. A short stubshaft 82 carrying the spur gear 76 at one end is received at itsopposite end within the drum portion 86 and pin connected thereto. Withthis arrangement, it will be noted that the cam shaft 74 rotates underthe influence of the Worm wheel 26, even when the output shaft 22 isstationary and slippage is taking place in the torque limiting clutch18.

The cams 70 and 72 are releasably secured on the cam In the illustrativecase, the cams are held in place by a nut 84 threadedly engaged on theend of the shaft74 and urging them into forceful frictional engagementwith one another and the stop shoulder on the shaft. To adjust therelative positions of the cams 70 and 72, it is simply necessary to backoff the nut 84, thereby freeing them for relative movement on the shaft22.

The switches 66 and 68 are mounted on the housing 64 and disposed withtheir actuating buttons in the movement paths of their associated cams70 and 72, respectively. The switch 66 is connected to the energizingcircuit of the motor, which produces clockwise rotation of the outputshaft 22 and is arranged when actuated to deenergize that motor circuit.Likewise, the other switch 68 is connected in the counterclockwisecircuit of the motor and arranged to de-energize that motor circuit.

By appropriate adjustment of the earns 70 and 72 on their'shaft 74, theactuator 10 can be conditioned so that its clockwise andcounterclockwise motions cease substantially at the moment the drivendevice reaches its mechanical limits. In this connection, when the motor12 is energized to produce rotation of the output shaft 22 in a givendirection, the worm 28 drives the worm wheel 26" and, in turn, theoutput shaft 22 through the torque limiting clutch 18. During suchoperation, the worm wheel 26 also drives the cam shaft 74 to move one ofthe cams toward its associated switch. When the cam engages its switchas, for example, in the manner illustrated in FIGURE 2, motor operationceases, and no further shaft rotation in that direction can take place,as long as the switch is actuated. In the event of a failure of thelimiting mechanism 20, as by malfunctioning of one of the switches 66and 68, the torque limiting clutch 18 serves to protect the actuator, aswell as the driven device, in the manner explained above. Moreover, themotor 12 will then continue to operate without damage to the variousparts, until it is manually de-energized. In this situation, the camshaft 74, of course, continues to rotate under the influence of the wormwheel 26, however, no damage to the limiting mechanism occurs, as thecams are shaped so as to permit them to move on past their respectiveswitches. Upon remedying the malfunction, the cams, of course, can bereadjusted to coordinate the limit positions of the actuator with thelimits of the driven device, because the cams will be undamaged by suchmalfunction.

A feature of the present actuator is that adjustment of the cams to makethe limit positions of the actuator correspond to the limits of thedriven device, may be facilitated by making use of the torque limitingclutch 18. In this regard, the actuator is first operated to move thedriven device into one of its mechanical limits in such a sequence thatthe limit is reached before the corresponding switch as, for example,the clockwise switch 66 is actuated by its cam 70. Once the mechanicallimit is reached, the output shaft 22 is blocked, but because of theoperation of the clutch 18, the cam 70 continues to move toward itsswitch 66. Upon switch actuation by the cam 70, the motor 12 isde-energized in the clockwise direction.

The next step of this adjustment procedure is to coordinate thecounterclockwise limit position of the actuator to the oppositemechanical limit of the driven device. This may be done by operating theactuator in the counterclockwise direction with the cam 70 fixed in anadjusted position on the shaft, and the cam 72 either loose on theshaftor positioned so that the mechanical limit of the driven device isreached before the counterclockwise switch 68 is actuated. Just as thedriven device reaches its opposite limit position, as evidenced by thetorque limiting clutch 18 beginning to slip, the motor 12 is manuallyde-energized. The cam 72 is then moved into actuating relationship withits switch 68 and fixed on the shaft 74, whereupon the two cams will bematched with the limits of the driven device. Alternately, the finalstep may be accomplished by temporarily shorting out the switch 68 andpositioning the cam 72 in actuating relationship with that switch. Theactuator is next energized in a counterclockwise direction until thelimit position of the driven device is reached. Since in this case thecam is already positioned, it is merely necessary as a final step totighten the nut when the shaft is properly aligned.

In order that the switches will operate just slightly before the drivendevice actually moves fully into its limit positions, final preciseadjustment of the cams 70 and 72 normally is accomplished manually.However, the adjustment feature described above is particularlyadvantageous in initially obtaining approximate coordination of thelimit positions of the actuator with the mechanical limits of the drivendevice.

Because of the particular gear connection provided between the Wormwheel 26 and the cam shaft 74, the shaft makes a complete revolution forevery few revolutions of the output shaft 22. This stems from the factthat the illustrative embodiment of the invention has a fairly high stepdown gear ratio between its drive motor and output shaft. In someapplications, it may be desirable to provide an output shaft with agreater range of travel. If so, this may be achieved by providing asuitable gear train between the worm wheel 26and the cam shaft 74.

Although one embodiment of the invention has been illustrated anddescribed with a certain degree of particularity, it will be understoodthat this was only by way of illustration and that various changes inthe details of the construction and arrangement of the various parts maybe made without departing from the spirit and scope of the invention.

I claim:

1. In an actuator having a reversible motor for moving a driven devicebetween opposite mechanical limits, apparatus comprising:

' an output shaft adapted to be coupled to said driven device;

a rotatable drive member coupled to said motor;

a sleeve secured to said drive member and disposed in coaxial spacedrelation with said shaft; 1

a pair of shaft disks disposed around said output shaft and keyedthereto for rotation with said shaft;

a sleeve disk interposed between said shaft disks and arranged with itsopposite side faces in engagement with adjacent faces of said shaftdisks, said sleeve disk being keyed to said sleeve for rotationtherewith;

spring means on said shaft yieldably urging the engaged faces of saidshaft disks and sleeve disk into frictional contact, whereby said shaftrotates with said sleeve when the torque on said shaft is below apredetermined maximum; and

a limiting mechanism associated with said motor and including mechanicalmeans connected to and driven by said drive member independently of saidshaft, said limiting mechanism having limiting means stopping said motorwhen said drive member has turned through the number of revolutions in agiven direction necessary to move the driven device from one to theother of its mechanical limits. 7

2. In an actuator having a reversible motor for moving a driven devicebetween opposite mechanical limits, apparatus comprising:

a housing;

an output shaft rotatably mounted in said housing with a portionprojecting exteriorly thereof;

a drive member rotatably mounted in said housing and coupled to saidmotor;

a sleeve secured to said drive member and disposed in coaxial spacedrelation with said shaft;

slip clutch means coupling said sleeve to said shaft so that they rotatetogether when the torque on said shaft is below a predetermined maximum;

means associated with said slip clutch means and accessible exteriorlyof said housing for adjustably establishing said predetermined maximumtorque; and

a limiting mechanism associated with said motor and including mechanicalmeans connected to and driven by said drive member independently of saidshaft, said limiting mechanism having limiting means stopping said motorwhen said drive member has turned through the number of revolutions in agiven direction necessary to move the driven device from one to theother of its mechanical limits.

3. In an actuator having a reversible motor for moving a driven devicebetween opposite mechanical limits, apparatus comprising:

a housing;

an output shaft rotatably mounted in said housing with a portion thereofprojecting exteriorly thereof;

a drive member rotatably mounted in said housing, said member beingrotatable about an axis oriented coaxial with that of said shaft;-

a sleeve secured to said drive member and disposed in coaxial spacedrelation with said shaft;

a pair of shaft disks mounted on said shaft in side-byside relation andkeyed thereto for rotation with said shaft;

a sleeve disk disposed around said shaft and between said shaft disks inface-to-face engagement, said sleeve disk being keyed to said sleeve forrotation therewith;

means carried by said shaft and movable axially thereof forurging' saidengaged faces of said shaft disks and sleeve disk into forcefulfrictional contact, whereby said shaft rotates with said sleeve when thetorque on said shaft is below a predetermined maximum;

means operatively associated with said urging means and accessibleexteriorly of said housing for adjusting the force urging said engagedfaces into such frictional contact;

and a limiting mechanism associated with said motor and includingmechanical means connected to and driven by said drive memberindependently of said shaft, said limiting mechanism having limitingmeans stopping said motor when said drive member has turned through thenumber of revolutions in a given direction necessary to move the drivendevice from one to the other of its mechanical limits.

4. In an actuator having a reversible motor for moving a driven devicebetween opposite mechanical limits, apparatus comprising:

an output shaft;

a rotatable drive member coupled to said motor;

slip clutch means coupling said drive member to said output shaft;

switch means for stopping operation of said motor;

a cam shaft, mechanical means connecting said cam shaft to said drivemember, whereby said cam shaft is operated by said drive member;

and a pair of cams adjustably mounted on said cam shaft, each of saidcams actuating said switch means when said drive member has turnedthrough the number of revolutions .in a given direction necessary tomove the driven device from one to the other of its mechanical limits,said slip cl-utch means permitting continued rotation of said drivemember and said cam shaft when said driven device is in its mechanicallimits and said output shaft is blocked, whereby said cams may beadjusted on said cam shaft to produce actuation ofsaid switch meanscoincidental with said driven device reaching its mechanical limits.

5. In an actuator having a reversible motor for moving a driven devicebetween its mechanical limits, apparatus comprising:

an output shaft;

a drive member rotatably mounted on said output shaft and coupled tosaid motor;

a sleeve secured to one face of said drive member and disposed incoaxial relation with said output shaft, said sleeve having its innerperiphery spaced from the periphery of said output shaft;

slip clutch means coupling said sleeve to said output shaft;

switch means for stopping operation of said motor;

a cam shaft, mechanical means connecting said cam shaft to said drivemember, whereby said cam shaft is operated by said drive member;

and adjustable switch actuating means operable by said cam shaft toactuate said switch means when said drive member has turned through thenumber of revolutions in a given direction necessary to move the drivendevice from one to the other of its mechanical limits, said switch slipclutch means permitting continued rotation of said drive member whensaid driven device is in its mechanical limits and the output shaft isblocked, whereby the positions of actuation of said switch means may becorrelated with the mechanical limits of said driven device.

References Cited by the Examiner UNITED STATES PATENTS BERNARD A.GILHEANY, Primary Examiner.

O. L. RADER, Examiner.

R. COOKE, T. MACBLAIN, H. E. SPRINGBORN,

Assistant Examiners.

4. IN AN ACTUATOR HAVING A REVERSIBLE MOTOR FOR MOVING A DRIVEN DEVICEBETWEEN OPPOSITE MECHANICAL LIMITS, APPARATUS COMPRISING: AN OUTPUTSHAFT; A ROTATABLE DRIVE MEMBER COUPLED TO SAID MOTOR; SLIP CLUTCH MEANSCOUPLING SAID DRIVE MEMBER TO SAID OUTPUT SHAFT; SWITCH MEANS FORSTOPPING OPERATION OF SAID MOTOR; A CAM SHAFT, MECHANICAL MEANSCONNECTING SAID CAM SHAFT TO SAID DRIVE MEMBER, WHEREBY SAID CAM SHAFTIS OPERATED BY SAID DRIVE MEMBER; AND A PAIR OF CAMS ADJUSTABLY MOUNTEDON SAID CAM SHAFT, EACH OF SAID CAMS ACTUATING SAID SWITCH MEANS WHENSAID DRIVE MEMBER HAS TURNED THROUGH THE NUMBER OF REVOLUTIONS IN AGIVEN DIRECTION NECESSARY TO MOVE THE DRIVEN DEVICE FROM ONE TO THEOTHER OF ITS MECHANICAL LIMITS, SAID SLIP CLUTCH MEANS PERMITTINGCONTINUED ROTATION OF SAID DRIVE MEMBER AND SAID